DESCRIPTION: (Applicant's Abstract) The primary aims of the proposed study are to: 1) investigate the efficacy of Structural Ecosystems Therapy (SET) in reducing adolescent drug use and conduct problems, and 2) examine it's theoretical mechanisms of action. SET is a culturally sensitive comprehensive ecosystemic intervention that systematically targets maladaptive patterns of interaction at three levels of the adolescent's social ecology: microsystem (family, peers, school, and justice system), mesosystem (family-peer, family-school, and family-justice system), and exosystem (parental support system). It is hypothesized that improvements in functioning at these three levels will lead to: 1) reductions in symptomatic behaviors of a) drug use, and b) conduct, delinquent, and antisocial behaviors; and 2) improvements in psychosocial functioning. An experimental design is achieved by randomly assigning 312 (156 African-American, 156 Hispanic) drug using, behavior problem adolescents to one of three treatment conditions: SET, Structural family therapy (FAM), and community control (CC). FAM represents one standard of care in the treatment of drug using, behavior problem adolescents, and CC is intended to replicate the typical range of services currently provided in our community. Three rigorous procedures are designed to ensure fidelity to conditions. Comprehensive assessments of adolescent drug use, conduct problems, and functioning at each of the three ecosystemic levels are conducted at baseline, and 6, 12, and 18 months post-baseline. Analyses investigate the intervention's direct effects on behavioral outcomes (drug use, conduct problems, and psychosocial functioning), and hypothesized mediators (micro-, meso-, and exosystemic functioning), as well as the contribution of each mediator to outcome. Proposed analyses include RMANOVA, structural equations modeling, and Hierarchical Linear Modeling. Additional analyses explore the moderating effects of race/ethnicity, culture, treatment adherence, and treatment dosage.